Image Decoding With Adaptive Chroma Quantization Tables

The patent segments the chroma quantization parameter derivation by component type (Cb and Cr), allowing different quantization parameters to be applied to different chroma components. This is achieved through separate flag fields (first chroma flag and second chroma flag) that independently control whether a chroma quantization parameter table is applied to each component, enabling fine-grained control over compression characteristics for different color information types.

The patent applies local quality by deriving and applying different quantization parameters specifically for chroma components based on their individual characteristics. Instead of using a uniform quantization parameter for all components, the system derives chroma-specific quantization parameters (first chroma quantization parameter for Cb, second chroma quantization parameter for Cr) that are optimized for the particular compression needs of chroma information.

The patent implements preliminary action by pre-defining chroma quantization parameter tables that can be derived from luma quantization parameter tables using predetermined rules. The system prepares multiple candidate chroma quantization parameters in advance based on flag combinations, so that during actual encoding/decoding, the appropriate pre-computed parameter can be directly selected without performing complex real-time calculations.

The patent applies parameter changes by systematically varying the chroma quantization parameter based on the state of chroma flags (first chroma flag and second chroma flag). The system derives different quantization parameters (first chroma quantization parameter, second chroma quantization parameter, or third chroma quantization parameter) depending on which flags are set, allowing adaptive parameter selection that balances compression efficiency with implementation complexity.